The present invention relates to an improved magnetic recording medium, such as a thin film magnetic recording disk, and to a method of manufacturing the medium. The invention has particular applicability to longitudinal magnetic recording media exhibiting high areal recording density, low noise, high SMNR, and high coercivity.
The continuously increasing requirements for thin film magnetic recording media with very high areal recording densities impose increasingly greater requirements on the magnetic properties of the various thin film layers constituting the media, such as increased remanent magnetic coercivity (Hr), and coercivity squareness (Sr*), low medium noise, e.g., expressed as signal-to-medium noise ratio (SMNR), and improved narrow track recording performance. As the areal recording density requirement increases, it becomes increasingly difficult to fabricate magnetic recording media, e.g., thin film longitudinal media, which satisfy each of these demanding requirements.
The linear recording density can be increased by increasing the Hr of the media; however, this objective can only be achieved by decreasing the media noise, as by formation and maintenance of magnetic recording layers with very finely dimensioned, non-magnetically coupled grains. Media noise is a dominant factor restricting obtainment of further increases in areal recording density of high density magnetic hard disk drives. The problem, or cause, of media noise is generally attributed, in large part, to inhomogeneous magnetic grain size and inter-granular exchange coupling. Accordingly, it is considered that, in order to increase linear recording density of thin film magnetic media, the media noise must be minimized by suitable control of the microstructure of the magnetic recording layer(s).
A portion of a conventional thin film, longitudinal magnetic recording medium 1, such as is commonly employed in hard disk form in computer-related applications, is depicted in FIG. 1 in simplified, schematic cross-sectional view, and comprises a substantially rigid, non-magnetic substrate 10, typically of aluminum (Al) or an aluminum-based alloy, such as an aluminum-magnesium (Alxe2x80x94Mg) alloy, or of glass, glass-ceramic, etc., having sequentially deposited or otherwise formed on a surface 10A thereof a plurality of thin film layers. When substrate 10 comprises Al or an Al-based alloy a plating layer 11, such as of amorphous nickel-phosphorus (Nixe2x80x94P), is typically initially provided on substrate surface 10A (such NiP plating layer 11 generally is omitted when substrate 10 comprises glass). The plurality of thin film layers formed over plating layer 11 or substrate surface 10A include a system 12 of layers for control of the microstructure of medium 1, comprising a first, or seed layer 12A of an amorphous or fine-grained material, e.g., a chromium-titanium (Crxe2x80x94Ti) alloy and a second, polycrystalline underlayer 12B, typically of Cr, a Cr-based alloy, or a B2-structured Nixe2x80x94Al alloy (as first described by Li-Lien Lee et al. in IEEE Transactions on Magnetics, 30 (6), 3951-3953 (1994)); a magnetic recording layer 13, e.g., of a cobalt (Co)-based alloy with one or more of platinum (Pt), Cr, boron (B), etc.; a protective overcoat layer 14, typically containing carbon (C), e.g., diamond-like carbon (xe2x80x9cDLCxe2x80x9d); and a lubricant topcoat layer 15, e.g., of a perfluoropolyether. Each of layers 11-14 may be deposited by suitable physical vapor deposition (xe2x80x9cPVDxe2x80x9d) techniques, such as sputtering, and layer 15 is typically deposited by dipping or spraying.
In operation of medium 1, the magnetic layer 13 is locally magnetized by a write transducer, or write xe2x80x9cheadxe2x80x9d, to record and thereby store data/information therein. The write transducer or head creates a highly concentrated magnetic field which alternates direction based on the bits of information to be stored. When the local magnetic field produced by the write transducer is greater than the coercivity of the material of the recording medium layer 13, the grains of the polycrystalline material at that location are magnetized. The grains retain their magnetization after the magnetic field applied thereto by the write transducer is removed. The direction of the magnetization matches the direction of the applied magnetic field. The magnetization of the recording medium layer 13 can subsequently produce an electrical response in a read transducer, or read xe2x80x9cheadxe2x80x9d, allowing the stored information to be read.
As indicated above, it is recognized that the magnetic properties which are critical to the performance of the magnetic recording. layer 13, i.e., Hr, Mr (magnetic remanence), S*, and SMNR, depend primarily on the microstructure of the magnetic recording layer 13 which, in turn, is strongly influenced by the microstructure of the underlying system 12 of seed and underlayers 12A and 12B, respectively. It is also recognized that underlayers having a very fine grain structure are highly desirable, particularly for growing fine grains of hexagonal close-packed (hcp) Co-based magnetic alloys deposited thereon.
Adverting to FIG. 2, a recent approach for improving the microstructure, texture, and crystallographic orientation of magnetic alloys in the fabrication of thin film, high recording density, longitudinal magnetic recording media 1xe2x80x2, involves modification of layer system 12 for microstructure control to include a third, intermediate (or xe2x80x9consetxe2x80x9d) layer 12C between underlayer 12B and magnetic recording layer 13. A number of Co-based alloy materials, such as CoCr, magnetic CoPtCr, CoPtCrTa, CoCrB, CoCrTa, and CoCrTaOx (where Ox indicates surface-oxidized CoCrTa), etc., have been studied for use as intermediate layers 12C according to such approach, as disclosed in, for example, U.S. Pat. Nos. 5,736,262; 5,922,442; 6,001,447; 6,010,795; 6,143,388; 6,150,016; 6,221,481 B1; and 6,242,086 B1, the entire disclosures of which are incorporated herein by reference.
Currently, the most widely utilized magnetic alloy for the active recording layer of thin film, high areal recording density, longitudinal media is high Pt, high B content CoCrPtB, i.e., with more than about 5 at. % each of Pt and B. However, the use of such high Pt, high B content CoCrPtB magnetic alloys presents several difficulties and drawbacks with respect to the design of high areal density, high SMNR media having a film structure similar to that of FIG. 2 including a layer system 12 for microstructure control, comprised of one or more of seed layer 12A, underlayer 12B, and intermediate layer 12C.
Specifically, as disclosed in commonly assigned U.S. Pat. No. 6,132,863 and U.S. patent application Ser. No. 09/497,524, filed Feb. 4, 2000, the entire disclosures of which are incorporated herein by reference, magnetic media can be advantageously fabricated with simultaneous crystallographic orientation and grain size refinement, by interposition of a xe2x80x9cdouble underlayerxe2x80x9d structure (equivalent to a structure represented as 12B1/12B2, wherein 12B1 and 12B2 respectively indicate first-deposited and second-deposited underlayers) between the substrate and the magnetic recording layer, e.g., a Cr/CrV or Cr/CrW double underlayer structure, with the Cr first underlayer (=12B1) being deposited directly on the substrate. Such media with a Cr first underlayer deposited directly on the substrate or via an intervening seed layer (=12A) exhibit high SMNR. However, the lattice mismatch between the Cr first underlayers and the high Pt, high B CoCrPtB magnetic recording layer is very large. In addition, since the typically utilized NiAl-based, B-2 structured underlayer 12B has lattice constants similar to that of the Cr underlayers 12B or 12B1, the difference in lattice constants between the NiAl-based underlayer 12B and the CoCrPtB recording layer(s) 13 is similarly large. More particularly, for good lattice matching, the (110) planes of Cr and NiAl should match with the (00.2) planes of Co. Therefore, the 2d values of these planes must be compared, where d is the spacing between planes. Specifically, the 2d values of the (110) plane of each of Cr and NiAl is 4.07 xc3x85, whereas the 2d values of representative Co (00.2) planes of high Pt, high B content CoCrPtB magnetic alloys CoCr16Pt10B10 and CoCr22Pt12B6 are 4.189 and 4.193 xc3x85, respectively (wherein the subscripts in each case indicate atomic percent).
In addition to the above disadvantage associated with the use of high Pt, high B content CoCrPtB magnetic alloys with the enumerated seed and underlayer materials, the CoCrTa-based alloys typically utilized as an intermediate layer (12C) between the seed/underlayer system (12A/12B) and the recording layer 13 are not suitable for use with the currently utilized CoCrPtB alloys in most instances. The difficulty arises from the tendency for high Cr content CoCrTa alloys, e.g., CoCr37Ta8, to promote undesirable Co (00.2) crystallographic texture in the CoCrPtB magnetic recording layer (13). Moreover, the use of CoCrTa alloys with lower Cr content, such as CoCr14Ta4, is problematic in that they have a much lower magnetic anisotropy than CoCrPtB, and as a consequence, the coercivity of the combined intermediate layer/magnetic layer (=12C/13) is not significantly enhanced. Also, the extremely small grain size of CoCrTa-based intermediate layers renders them susceptible to undesirable polarity reversal under very low magnetic fields.
In view of the foregoing, there exists a need for improved thin film intermediate layers and materials, as well as improved methods for their use in forming thin film, very high areal recording density, longitudinal magnetic recording media exhibiting high SMNR and utilizing CoCrPtB magnetic alloy materials for the active recording layer. Specifically, there exists a need for improved methods which can be readily and easily implemented for interposing an improved intermediate layer in thin film form between Cr-containing or B2-structured underlayers and high Pt, high B content CoCrPtB magnetic alloy recording layers, in order to maintain good Co (11.0) or (10.0) crystallographic orientation of the latter, with attendant good magnetic recording performance at high SMNR.
The present invention, therefore, addresses and solves problems attendant upon forming thin film, high areal recording density, high SMNR, longitudinal magnetic recording media including high Pt, high B content CoCrPtB alloy recording layers and Cr-based or B2-structured underlayers, e.g., in the form of hard disks, which media utilize substantially non-magnetic, high Cr content CoCrPt intermediate layers for promoting and maintaining Co (11.0) or (10.0) crystallographic orientation of the CoCrPtB alloy recording layers, while affording full capability with all technical and economic aspects of conventional automated manufacturing technology for the fabrication of magnetic recording media.
An advantage of the present invention is an improved, low noise, high areal recording density, longitudinal magnetic recording medium.
Another advantage of the present invention is a method of manufacturing an improved low noise, high areal recording density, longitudinal magnetic recording medium.
Additional advantages and other features of the present invention will be set forth in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the present invention. The advantages of the present invention may be realized as particularly pointed out in the appended claims.
According to an aspect of the present invention, the foregoing and other advantages are obtained in part by a magnetic recording medium, comprising in overlying sequence from a surface of a non-magnetic substrate:
at least one Cr-containing or B2-structured underlayer;
a substantially non-magnetic CoCrPt alloy intermediate layer; and
at least one CoCrPtB ferromagnetic alloy recording layer; wherein the intermediate layer of substantially non-magnetic CoCrPt alloy has a composition which facilitates Co (11.0) or (10.0) crystallographic orientation of the at least one CoCrPtB ferromagnetic alloy recording layer.
According to embodiments of the present invention, the at least one CoCrPtB ferromagnetic alloy recording layer contains at least about 5 at. % each of Pt and B and the intermediate layer of substantially non-magnetic CoCrPt alloy has a lattice constant which reduces the effect of lattice constant mismatch between the at least one Cr-containing or B2-structured underlayer and the at least one CoCrPtB ferromagnetic alloy recording layer; the intermediate layer of substantially non-magnetic CoCrPt alloy has a thickness from about 10 to about 45 xc3x85, and contains from about 28 to about 43 at. % Cr and from about 4 to about 15 at. % Pt.
In accordance with certain exemplary embodiments of the present invention, the intermediate layer of substantially non-magnetic CoCrPt alloy is CoCr37Pt5 or CoCr30Pt9.
According to further embodiments of the present invention, the medium is a bi-crystal or uni-crystal medium and further comprises a seed layer intermediate the non-magnetic substrate and the at least one Cr-containing or B2-structured underlayer, the at least one seed layer being selected from the group consisting of Cr/NiPOx, CrTi, and NiAlOx.
According to certain embodiments of the present invention, the at least one Cr-containing or B2-structured underlayer is selected from the group consisting of: Cr, CrW, CrMo, and CrV (each body-centered cubic, i.e., xe2x80x9cBCCxe2x80x9d); NiAl, NiAlTi, and NiAlRu (each B2-structured); and double-layer structures such as Cr/CrW, Cr/CrV, and NiAl/CrMo.
According to other embodiments of the present invention, the magnetic recording medium further comprises a protective overcoat layer over the ferromagnetic recording layer and a lubricant topcoat over the protective overcoat layer.
Another aspect of the present invention is a method of manufacturing a magnetic recording medium, which method comprises the sequential steps of:
(a) providing a non-magnetic substrate having a surface;
(b) forming at least one Cr-containing or B2-structured underlayer on the substrate surface;
(c) forming a substantially non-magnetic CoCrPt alloy intermediate layer over the at least one Cr-containing or B2-structured underlayer; and
(d) forming at least one CoCrPtB ferromagnetic alloy recording layer over the substantially non-magnetic CoCrPt alloy intermediate layer;
wherein step (c) comprises forming the intermediate layer of substantially non-magnetic CoCrPt alloy with a composition which facilitates Co (1 1.0) or (10.0) crystallographic orientation of the at least one CoCrPtB ferromagnetic alloy recording layer.
In accordance with various embodiments of the present invention, step (a) comprises providing a non-magnetic substrate selected from the group consisting of Al, Alxe2x80x94Mg alloys, other Al-based alloys, NiP-plated Al, NiP-plated Al-based alloys, glass, ceramics, glass-ceramics, polymers, and laminates or composites thereof; step (b) comprises forming the at least one Cr-containing or B2-structured underlayer from the group consisting of Cr, CrW, CrMo, CrV, Cr/CrV, Cr/CrW, NiAl, NiAlTi, NiAlRu, and NiAl/CrMo; step (c) comprises forming an about 10 to about 45 xc3x85 thick, substantially non-magnetic CoCrPt alloy intermediate layer containing from about 28 to about 43 at. % Cr and from about 4 to about 15 at. % of Pt, the intermediate layer of substantially non-magnetic CoCrPt alloy having a lattice constant which reduces the effect of lattice constant mismatch between the at least one Cr-containing or B2-structured underlayer and the at least one CoCrPtB ferromagnetic alloy recording layer; and step (d) comprises forming at least one CoCrPtB ferromagnetic alloy recording layer containing at least about 5 at. % each of Pt and B.
According to certain embodiments of the present invention, the method further comprises a step of forming a seed layer on the non-magnetic substrate prior to performing step (b) for forming the at least one Cr-containing or B2-structured underlayer, the at least one seed layer being selected from the group consisting of Cr/NiPOx, CrTi, and NiAlOx.
In accordance with further embodiments of the present invention, the method further comprises the sequential steps of:
(e) forming a protective overcoat layer over the ferromagnetic recording layer; and
(f) forming a lubricant topcoat over the protective overcoat layer.
Embodiments of the present invention include performing at least depositing steps (b)-(d) by sputtering.
Still another aspect of the present invention is a magnetic recording medium, comprising:
at least one Cr-based or B2-structured underlayer and at least one CoCrPtB ferromagnetic recording layer containing at least about 5 at. % each of Pt and B; and
means for facilitating Co (11.0) or (10.0) crystallographic orientation of the at least one CoCrPtB ferromagnetic alloy recording layer.
In accordance with embodiments of the present invention, the medium further comprises a non-magnetic substrate for supporting the underlayer, ferromagnetic recording layer, and the means for facilitating.
Additional advantages and aspects of the present invention will become readily apparent to those skilled in the art from the following detailed description, wherein embodiments of the present invention are shown and described, simply by way of illustration of the best mode contemplated for practicing the present invention. As will be described, the present invention is capable of other and different embodiments, and its several details are susceptible of modification in various obvious respects, all without departing from the spirit of the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not limitative.